[CMake] Cannot determine link language for target

[Marc-André Laverdière]

Hello CMakers,

I'm really a n00b...

So, I am building each subdirectory into a static library and I want to
put all those libraries into a nice big dynamic library. The big dynamic
library is the objective here.

I'm doing it as such:
ADD_LIBRARY(XYZ SHARED
${CMAKE_CURRENT_SOURCE_DIR}/stdio/libstdio.a
${CMAKE_CURRENT_SOURCE_DIR}/stdlib/libstdlib.a
${CMAKE_CURRENT_SOURCE_DIR}/string/libstring.a
${CMAKE_CURRENT_SOURCE_DIR}/time/libtime.a
${CMAKE_CURRENT_SOURCE_DIR}/wchar/libwchar.a)

Yet, I obtain the following, when I run rebuild_cache:
CMake Error: Cannot determine link language for target XYZ

What am I doing wrong? How should I proceed to build that dynamic library?

Thanks in advance for the patience and the support!
--
Marc-André LAVERDIÈRE, B. Eng., M. A. Sc. (in progress)
Research Assitant - Computer Security Laboratory
CIISE, Université Concordia University, Montréal, Québec, Canada
www.ciise.concordia.ca

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"Perseverance must finish its work so that you may be mature and
complete, not lacking anything." -James 1:4

[Brad King]

Post by Marc-André Laverdière
Hello CMakers,
I'm really a n00b...
So, I am building each subdirectory into a static library and I want to
put all those libraries into a nice big dynamic library. The big dynamic
library is the objective here.
ADD_LIBRARY(XYZ SHARED
${CMAKE_CURRENT_SOURCE_DIR}/stdio/libstdio.a
${CMAKE_CURRENT_SOURCE_DIR}/stdlib/libstdlib.a
${CMAKE_CURRENT_SOURCE_DIR}/string/libstring.a
${CMAKE_CURRENT_SOURCE_DIR}/time/libtime.a
${CMAKE_CURRENT_SOURCE_DIR}/wchar/libwchar.a)
CMake Error: Cannot determine link language for target XYZ
What am I doing wrong? How should I proceed to build that dynamic library?

CMake needs to know what programming language is used within the target.
This determines whether the C or C++ compiler (or Fortran, etc.) is
used to link the shared library. Normally the language is computed from
the language of the source files listed in the target. Since you don't
list any source files CMake cannot deduce the language. You can set it
explicitly by setting the LINKER_LANGUAGE target property:

SET_TARGET_PROPERTIES(XYZ PROPERTIES LINKER_LANGUAGE C)

Linking static libraries into a shared library is generally a dangerous
thing to do anyway. What are you trying to accomplish? Why can't you
just list all the source files from those subdirectories in the XYZ target?

-Brad

[Marc-André Laverdière]

Dear Brad, William,

Thanks for the quick reply.

SET_TARGET_PROPERTIES did the trick.

I don't know enough of industrial UNIX programming to know why what I
did was a bad thing. I'll need a lecture :)

Orginally, we were compiling each subdir in a .a file so that we could
compile unit tests and link them only with the .a file(s) needed. At
that stage, we didn't go much farther than some test programs that used
a module or two, so we didn't need to put all things together in a big .so.

I figured that keeping this in CMake would keep things lighter. That
being said, we can also have the tests dynamically linking to the .so

I'm making those modifications. However, I'd like to avoid having to put
the whole subdirectory hierarchy before each file... that'd make things
heavy (especially since one thing I'm adding soon is gonna have things 3
levels down...). Is there a way to do that outside of the
non-reccomended AUX_SOURCE_DIRECTORY?

Regards,
--
Marc-André LAVERDIÈRE, B. Eng., M. A. Sc. (in progress)
Research Assitant - Computer Security Laboratory
CIISE, Université Concordia University, Montréal, Québec, Canada
www.ciise.concordia.ca

/"\
\ / ASCII Ribbon Campaign
X against HTML e-mail
/ \

"Perseverance must finish its work so that you may be mature and
complete, not lacking anything." -James 1:4

Post by Brad King

Post by Marc-André Laverdière
Hello CMakers,
I'm really a n00b...
So, I am building each subdirectory into a static library and I want to
put all those libraries into a nice big dynamic library. The big dynamic
library is the objective here.
ADD_LIBRARY(XYZ SHARED
${CMAKE_CURRENT_SOURCE_DIR}/stdio/libstdio.a
${CMAKE_CURRENT_SOURCE_DIR}/stdlib/libstdlib.a
${CMAKE_CURRENT_SOURCE_DIR}/string/libstring.a
${CMAKE_CURRENT_SOURCE_DIR}/time/libtime.a
${CMAKE_CURRENT_SOURCE_DIR}/wchar/libwchar.a)
CMake Error: Cannot determine link language for target XYZ
What am I doing wrong? How should I proceed to build that dynamic library?

CMake needs to know what programming language is used within the target.
This determines whether the C or C++ compiler (or Fortran, etc.) is
used to link the shared library. Normally the language is computed from
the language of the source files listed in the target. Since you don't
list any source files CMake cannot deduce the language. You can set it
SET_TARGET_PROPERTIES(XYZ PROPERTIES LINKER_LANGUAGE C)
Linking static libraries into a shared library is generally a dangerous
thing to do anyway. What are you trying to accomplish? Why can't you
just list all the source files from those subdirectories in the XYZ target?
-Brad

[William A. Hoffman]

Post by Marc-André Laverdière
Hello CMakers,
I'm really a n00b...
So, I am building each subdirectory into a static library and I want to put all those libraries into a nice big dynamic library. The big dynamic library is the objective here.
ADD_LIBRARY(XYZ SHARED
${CMAKE_CURRENT_SOURCE_DIR}/stdio/libstdio.a
${CMAKE_CURRENT_SOURCE_DIR}/stdlib/libstdlib.a
${CMAKE_CURRENT_SOURCE_DIR}/string/libstring.a
${CMAKE_CURRENT_SOURCE_DIR}/time/libtime.a
${CMAKE_CURRENT_SOURCE_DIR}/wchar/libwchar.a)
CMake Error: Cannot determine link language for target XYZ
What am I doing wrong? How should I proceed to build that dynamic library?
Thanks in advance for the patience and the support!

You can not create a shared library by just adding a bunch of .a libraries.
You need source files. CMake is trying to compile the .a files which it
of course does not know how to do. What exactly are you trying to do?


-Bill